A downhole tool containing a radiation generator is useful for determining properties of a subsurface formation. Such a downhole tool may be inserted into a borehole drilled into the subsurface formation, and then emit radiation from its radiation generators. This radiation may travel into the subsurface formation and interact with constituents of the subsurface formation. These interactions may result in the emission of gamma rays or neutrons from the subsurface formation, and the downhole tool may have radiation detectors to detect this emitted radiation. Data from the radiation detectors may then be analyzed and used to determine properties of the subsurface formation.
Some radiation generators used by downhole tools may be neutron generators. A neutron generator may function by creating ions from deuterium and/or tritium gas, and then accelerating those ions through an acceleration column and toward a target. When the ions strike the target, neutrons may be generated.
While such radiation generators are useful, some drawbacks remain. For example, deleterious collisions between the ions and gas molecules in the acceleration column may occur, which may ultimately result in sputtering of components and lead to damage to parts of the radiation generator. Therefore, ways to reduce the number of these deleterious collisions are desirable.